Concrete form

ABSTRACT

A concrete form used in forming a contraction joint between adjacent concrete slabs and a sheet member therefor. The concrete form comprises a plurality of aligned stakes and an elongated relatively rigid sheet member. Each of the stakes includes a ledge means. The sheet member has upper and lower longitudinally extending, generally planar portions and a longitudinally extending key deformation portion interposed between and connected to said planar portions. The sheet member has a plurality of longitudinally spaced strap means formed within one of the planar portions. Each of the strap means is disposed at least in partial encompassing engagement around a portion of a corresponding one of the stakes. The sheet member also includes a ledge engaging means for engaging the ledge means of the stake. The sheet member also has one of the planar portions, prior to installation upon the stakes, convergently disposed toward the other planar portion, taken in a direction preceding from the stakes to the key deformation portion. The strap means, ledge means, ledge-engaging means and planar portions cooperate to hold said member against said stakes to prevent vertical movement of the member relative to the stakes.

United States Patent [72] inventor [54] CONCRETE FORM Primary Examiner.l. Spencer Overholser Assistant Examinerl.ucius R. Frye Attorney-Sheridan, Ross & Burton ABSTRACT: A concrete form used in forming a contraction joint between adjacent concrete slabs and a sheet member therefor. The concrete form comprises a plurality of aligned stakes and an elongated relatively rigid sheet member. Each of the stakes includes a. ledge means. The sheet member has upper and lower longitudinally extending, generally planar portions and a longitudinally extending key deformation portion interposed between and connected to said planar portions. The sheet member has a plurality of longitudinally spaced strap means formed within one of the planar portions. Each of the strap means is disposed at least in partial encompassing engagement around a portion of a corresponding one of the stakes. The sheet member also includes a ledge engag ing means for engaging the ledge means of the stake. The sheet member also has one of the planar portions, prior to installation upon the stakes, convergently disposed toward the other planar portion, taken in a direction preceding from the stakes to the key deformation portion. The strap means, ledge means, ledge-engaging means and planar portions cooperate to hold said member against said stakes to prevent vertical movement of the member relative to the stakes.

FIG. 9

Fl INVENTOR. G 5 7 Duane C. Burton FIG. 4

ATTORNEYS CONCRETE FORM BACKGROUND OF THE INVENTION Heretofore, many concrete forms of the type used in forming a key contraction joint between adjacent concrete slabs have been proposed, especially for monolithically poured concrete slabs. Many of these forms have had useful application. However, each of these forms has suffered from one or more disadvantages. For example, many of the prior art forms were disadvantageous in that a considerable. amount ofexpense and time were required to install same. Additionally, many prior art concrete forms were disadvantageous due to the fact that they could not be used in concrete slabs subjected to relatively large loads without spalling occurring. There are two distinct problems encountered in installing or erecting a concrete form. First, it is important that the concrete form be of a construction which will permit a single person to install a predetermined length of sheet member upon the stakes (which have already been installed'in the subgrade) in essentially a single operation. The other problem is to insure that the sheet member is secured relative to the stakes in a manner which will prevent the sheet member from floating upwardly within the mass of concrete following pouring thereof. For example, with many prior art concrete forms it has been and continues to remain the practice of securing the joint member to the supporting stakes upon which same is mounted by the use of screws, wires, or other suitable fastening devices.

SUMMARY OF TI-IE INVENTION This invention overcomes the disadvantages of the prior art forms by providing a concrete form comprising a plurality of spaced-apart; aligned stakes, each of said stakes including a ledge means, said stakes adapted to be driven .to a predetermined height so that the tops thereof are disposed along a predetermined grade level, and an elongated rigid sheet material member having upper and lower longitudinally extending, generally coplanar portions and a longitudinally extending key deformation portion interposed between and connected to said planar portion, said member having a plurality of longitudinally spacedstrap means formed within one s said planar portions, the spacing of said strap means corresponding to the longitudinal spacing of said stakes, each of said strap means being disposed at least in partial encompassing engagement about a portion of a corresponding one of said stakes, said member also including ledge-engaging means for engaging the ledge means of said stakes, said strap means, ledge means, and ledge-engaging means cooperating to support said member to prevent vertical movement of said member relative to said stakes. The sheet member is formed with one of the planar portions, prior to installation upon said stakes, being convergently disposed toward the other said planar portion.

Accordingly, a principal object of this invention is to provide a concrete form wherein the joint-forming member thereof is quickly and easily mounted upon a plurality of aligned vertical stakes by a single person in one easy operation and in a manner to prevent vertical movement of said member relative to said stakes but without involving the time consuming operation required in the use of screws, wires or the like.

Another object of this invention is to provide an improved concrete form of the type used in forming a key contraction join between adjacent concrete slabs which may be installed in the field more rapidly than many prior art concrete forms.

Another object of this invention is to provide a concrete form which may be easily and quickly installed in a manner that the joint forming member thereof resists any tendency to float upwardly under the influence of the pressure existing within the concrete following the pouring thereof.

Another object of this invention is to provide a concrete form in which the sheet member thereof includes a pair of coplanar portion one of which is biased toward the other thereby increasing frictional engagement between said sheet member when same is installed upon supporting stakes.

Another object of this invention is to provided a concrete form which is constructed without the use of an inverted U- shaped pocket formed adjacent the upper portion thereof and, thus, can be used to support relatively heavy loads thereon without spalling, cracking or the like.

Another object of this invention is to provide a concrete form of the type as aforedescribed in which the strap means are formed within the upper planar portion of the sheet member and one of the planar portions of the sheet member prior to installation of said member upon said stakes, is convergently disposed toward the other said planar portion, taken in a direction proceeding from said stakes toward said key deformation portion, whereby said strap means, ledge means, ledge-engaging means and planar portions cooperate to hold said member against said stakes to prevent vertical movement of said member relative to said stakes.

Another object of this invention is to provide a concrete form of the type as aforedescribed in which each of the strap means includes a lower surface and said ledge-engaging means comprises the lower surfaces of said strap means.

Another object of this invention is to provide a concrete form of the type as aforedescribed in which a portion of each of said strap means is disposed in contacting engagement with one side of a corresponding one of said stakes, said portion of said strap means including a generally vertically disposed part that is convergently disposed, taken in a direction proceeding toward the upper part of said member, with respect to said upper planar portion.

Another object of this invention is to provide a concrete form of the type as aforedescribed in which said ledge means includes a tab portion transversely disposed with respect to said stakes and said ledge-engaging means comprises a plurality of longitudinally spaced apertures, each of said apertures having a corresponding one of said tab portions disposed therein. I

Another object of this invention is to provide a concrete from of the type as aforedescribed in which the ledge means includes a tab portion transversely disposed with respect to said stake and said ledge-engaging means comprises a longitudinally extending recess formed in said member, each of said tab portions being disposed within said recess.

Another object of this invention is to provide a concrete form of the type as aforedescribed in which said member also includes a plurality of longitudinally spaced strap means formed within said lower planar portion, each of said strap means having a lower surface and said ledge means comprising a tab portion transversely formed upon said stake, said ledge-engaging means comprising the lower surfaces of the strap means formed in the lower planar portion.

Another object of this invention is to provide a concrete form of the type as aforedescribed in which said member also includes a plurality of longitudinally spaced strap means formed within said lower planar portion, said ledge means comprises a tab portion transversely formed upon said stakes, and said ledge-engaging means comprises the lower surface of said lower planar portion.

Another object of this invention is to provide a concrete from of the type as aforedescribed in which the upper planar portion of said sheet member includes a folded over portion extending downwardly from the upper edge thereof and disposed against at least a part of said upper planar portion.

Another object of this invention is to provide a concrete form of the type as aforedescribed in which said sheet member includes means formed thereon for increasing the frictional force resisting movement of the sheet member relative to said stakes, said means including roughened surface portions formed on either of the contacting surfaces of said stakes or said member.

Another object of this invention is to provide a joint-forming member constructed for use with a plurality of spacedapart, generally vertically disposed, aligned stakes having a ledge means formed thereon, said member comprising upper and lower longitudinally extending generally planar portions means being adapted for partially encompassing a portion of the stake, said member also including ledge-engaging means for engaging the ledge means of the stakes, one of said planar portions being convergently disposed relatively toward the other one of said planar portions, taken in a direction proceeding toward said key deformation portion.

Another object of this invention is to provide a joint-forming member as aforedescribed in which said member also includes a plurality of longitudinally spaced strap means formed in said lower planar portion.

Another object of this invention is to provide a joint-forming member as aforedescribed in which the upper planar portion is disposed in a plane that intersects a plane in which is disposed said lower planar portion to form an included angle varying between approximately l65to 175 DESCRIPTION OF THE DRAWINGS Further objects and advantages of the invention will become apparent from the following description and claims and from the accompanying drawings wherein:

FIG. 1 is a vertical section through adjoining concrete slabs and a concrete form showing one embodiment of a concrete form constructed in accordance with the subject invention;

FIG. 2 is a right end elevational view of the concrete form shown in FIG. I, the concrete slabs being omitted for purposes of clarity;

FIG. 3 is an enlarged view showing the sheet member having a longitudinally extending recess formed therein and a tab portion of one of the stakes disposed within said recess;

FIG. 4 is a vertical section another embodiment of a concrete form constructed in accordance with the subject in vention;

FIG. 5 is a vertical section of the sheet material member shown in FIG. 4 before same has been installed upon the stakes;

FIG. 6 is an enlarged view showing one embodiment of the strap means disposed in encompassing engagement about one of the stakes;

FIG. 7 is a top plan view of the stake shown in FIG. 6;

FIG. 8 is a vertical section of another concrete form constructed in accordance with the subject invention;

FIG. 9 is an elevational view of the sheet material member shown in FIG. 8 prior to installation thereof upon the stakes; and

FIG. 10 is a partial view of another embodiment of the lower part of a concrete form constructed in accordance with the subject invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, in FIG. 1 is shown a vertical section through adjoining concrete slabs of a concrete section showing a preferred embodiment of a concrete form 10 constructed in accordance with the subject invention. The concrete form 10 is the type used in forming a key contraction joint between adjacent concrete slabs 12 and I4 and comprises a plurality of aligned stakes 16 (only one of which is shown) and an elongated relatively rigid sheet material member 18. Each of the stakes 16 includes a ledge means such as the transversely disposed tab portion 20. The stakes are adapted to be driven to a predetermined height so that the tops 22 thereof are disposed along a predetermined grade level, preferably below the upper surfaces of the concrete slabs 12 and 14.

The sheet member 18 has upper and lower longitudinally extending, generally planar portions 24 and 26 and a longitudinally extending, key deformation portion 28 disposed inter mediate said upper and lower planar portions 24 and 26. The sheet member 18 also includes a plurality of longitudinally I A-u spaced strap means 30 (only one of which is shown) formed within one of said planar portions, preferably the upper planar portion 24. The spacing of the straps means 30 corresponds to the longitudinal spacing of the stakes 16. Each of the strap means 30 is shown as being formed integrally with the upper planar portion 24 and is disposed at least in partial encompassing engagement about a portion of a corresponding one of the stakes. The sheet member 18 also includes ledge-engaging means for engaging the ledge means or, as shown in FIG. 1, the tab portion 20 of the stake 16. The ledge-engaging means is shown in FIGS. 1 and 2 as comprising a plurality of longitudinally spaced apertures 32 (only one of which is shown. Each of the apertures 32 has a corresponding one of the tab portions 20 disposed therein. The sheet member 18 also includes a folded over portion 34 extending downwardly from the upper edge 36 of said sheet member 18 and disposed against at least a part of said upper planar portion 24. One of the surfaces of the stake or member is preferably roughened such as portion 37 of member 18, see FIG. 2, for the purpose of increasing the frictional interface between the member and the stakes. The strap means 30, the tab portions 20 and the apertures 32 cooperate to support the member R8 to prevent vertical movement of the member relative to the stakes.

In FIG. 3 is shown an enlarged view of a different ledge-engaging means, said ledge-engaging means comprising a longitudinally extending recess 38 formed in the sheet material member 40. The vertical height of the recess 38 at the entrance thereof is shown being substantially greater than the vertical height of the remaining portion of the recess 38. The purpose for this is to facilitate the installation of the sheet member with the tab portions 20 disposed within said recess 38.

In FIGS. 4-7 is shown another embodiment of a concrete form 42 constructed in accordance with the subject invention. The concrete form 42 is similar in certain respects to the concrete form 10 shown in FIG. 1. As is the case with concrete form shown in FIG. 1, the concrete form 42 comprises a plurality of stakes 44 (only one of which is shown) and a sheet material member 46. The stakes 44 differ from the stakes 16 in that the ledge means comprises a shelf 48, see FIGS. 6 and 7, formed immediately below the top 50 of the stakes 44. The stakes 44 preferably include a transversely disposed tab portion 52 located at a different vertical position than the tab portion 20 of the stake 16 shown in FIG. 1. Although it is preferred to use a stake 44 having a tab portion 52 as shown, the tab portion 52 may be deleted if desired.

The sheet material member 46 is similar in many respects to the sheet material member 18 shown in FIG. 1. The sheet material member 46 differs from the sheet material member 18 shown in FIG. I in that the upper planar portion 54, prior to installation of the sheet material member 46 upon stakes 44, is convergently disposed toward the lower planar portion 56, taken in a direction proceeding away from the stakes 44 toward the key deformation portion 58. The sheet material member 46 further differs from the sheet material member I8 shown in FIG. l in that a portion of each of the strap means 60 that is disposed in contacting engagement with one side of the corresponding one of the stakes 44 includes a generally vertically disposed part that is convergently disposed, taken in a direction proceeding toward the upper edge 62 of the upper planar portion 54. This construction is best shown in FIG. 6. The ledge-engaging means of the sheet material member 46 comprises the lower surface 64 of each of the strap means 60, see also FIG. 6. The sheet material member 58 also includes a plurality of handle means 63 (only one of which is shown) and a plurality of roughened surface portions (not shown) which may be formed in one or more places such as on the surface of the lower planar portion 56. As previously stated, the stakes 44 preferably includes tab portions 52 and the sheet material member 46 includes a plurality of apertures 66 (only one of which is shown). As illustrated in FIGS. 4 and 5, the apertures 66 are formed adjacent the upper part of the lower planar portion 56. The tab portions 52 and corresponding apertures 66,

where used, cooperate with the strap means 60, the convergently formed upper and lower planar portions 54 and 56 and roughened surface portions (where used) to support the sheet material member 46 to prevent vertical movement of said member 46 relative to the stakes 44.

The upper planar portion 54 of the sheet material member 46 lines in a plane which intersects a plane containing the lower planar portion 56 to form an included angle of approximately 165 to 177. It will be understood that a decrease in the size of this included angle will result in an increase in the amount of force urging the upper and lower planar portions 54 and 56 into contacting engagement with the adjacent sides of the stakes 54. With respect to the convergently formed strap portion 60 it will be understood that such construction further aids in securing the sheet material member 46 to the stakes 44 to prevent vertical movement of the sheet material member 46 relative to said stakes 44. As a matter of fact, as the sheet material member 46 is installed upon the stakes 44, the upper ends of the stakes 44 are virtually wedged between the strap means 60 and the adjacent surface of the upper planar portion 54.

In FIGS. 8 and 9 is shown another embodiment of a concrete form 68 constructed in accordance with the subject invention. The concrete form 68 comprises a plurality of stakes 70 (only one of which is shown) and an elongated sheet material member 72. The stakes 70 are substantially identical to the stakes 16 except for the vertical position of the tab portion 74 which, as shown, is located at an elevation slightly lower than the vertical elevation of the tab portions 20 as shown in FIG. 1 or the tab portions 52 as shown in FIG. 4.

The sheet material member 72 is similar to the sheet materialmember 46 shown in FIGS. 4 and 5 except that the strap means 76 shown in the upper planar portion 78 is similar to the strap means 30 of sheet material member 18 shown in FIG. land the lower planar portion 80 also includes strap means 82 formed therein. The ledge-engaging means of the sheet material member 72 comprises the lower surface 84 of the strap means 82. It will be understood that each strap means 82 lies in a vertical plane transversely disposed to the longitudinal axis of the member 72 and including therein a corresponding strap means 76. However, it will also be understood that the number of strap means 82 formed in the lower planar portion 80 does not necessarily have to equal the number of strap means 76 formed in the upper planar portion 78. The sheet material member 72 preferably includes roughened surface material member 72 preferably includes roughened surface portions (not shown) similar to roughened surface portions 37 formed in the sheet material member 18, see FIG. 2. The upper planar portion 78 of the sheet material member 72, prior to installation of said member 72 upon the stakes 70, is convergently disposed toward the lower planar direction 80, taken in a direction proceeding from said stakes 70 toward or into the recess formed by said key deformation portion 86. The sheet material member 72 also includes a plurality of handle means 85 (only one of which is shown).

In FIG. is shown a partial view of another embodiment of the lower part of concrete form constructed in accordance with the subject invention. The lower part of this concrete form is generally similar to the lower part of the concrete form 68 shown in FIG. 8 except that the tab portion 88 is formed upon the stake 90 at a vertical elevation below the elevation of the tab portion 74 formed on stake 70 as shown in FIG. 8. The sheet material member 72 is identical to the sheet material member shown in FIG. 8 and, thus, is identified with the same number. However, in connection with FIG. 10, the ledge-engaging means of the sheet material member 72 comprises the lower surface or lower edge 92 of the lower planar portion 80 of said sheet material member 72.

Referring now to FIGS. 1 and 2, installation of the concrete fonn 10 will now be described. A string or line (not shown) is stretched from side of the slot to be formed to the other side. Thestakes 16 are installed in a line along said string by being driven into the subgrade or subbase 94 until the tops 22 thereof are disposed along a predetermined grade level. Preferably, the tops 22 of the stakes 16 are disposed below the upper surface of the concrete slabs 12 and 14; however, it will be understood that the tops 22 may be disposed at the same level as the upper surfaces of the concrete slabs l2 and 14 if desired or required. The stakes 16 are longitudinally spaced apart along a predetermined line, generally by approximately 2 feet, although it will be understood that the distance separating the stakes may vary from that of 2 foot as circumstances dictate or require. Since the length of the strap means 30'and,

the apertures 32 are approximately two to three times the width of the stakes 16, it .will be understood that precise and accurate spacing of the stakes is not required. The spacing of the stakes 16 along the line as aforesaid may be effected with a suitable measuring means (not shown) or the sheet material member 18 may be laid adjacent said string or line and the spacing of the strap means 30 and apertures 32 used for determining the location of the stakes 16 along said line. After the stakes 16 have been installed in the subgrade 94 as aforedescribed, the sheet material member 18 is positioned with the strap means 30 thereof disposed vertically above the tops of the stakes 16. The positioning of the stakes in this manner is easily done by a single person in the field. The sheet material member 18 is then lowered such that the tops 22 of the stakes 16 are confined within or pass through the strap means 30. The sheet material member 18 is lowered to a position where the ledge means or tab portions 20 are disposed at the same level or elevation as the apertures 32. It will be understood that the lower part of sheet material member 18 must be pivoted slightly clockwise, as viewed in FIG. 1, to permit the lower part of sheet member 18 to clear the tab portions 20 which are to be disposed within the apertures 32. As soon as this occurs, the lower part of the sheet material member 18 is then pivoted clockwise, as viewed in FIG. 1, until the tab portions 20 are disposed within said apertures and lower planar portion 26 is disposed adjacent or in contacting engagement with the stakes 16. Thus, it will be readily appreciated that the concrete form 10 is of a construction which will pennit a single person to install a predetermined length of sheet material member 18 upon the stakes 16 in one easy operation and that sheet material member 18 can then be secured relative to the stakes in a manner which will prevent said sheet material member 18 from floating upwardly within the mass of concrete following pouring thereof but without having to use screws, wires or other fastening devices which require additional time to install and add to the overall cost of the materials involved.

Referring now to the concrete form 42 shown in FIG. 4, the stakes 44 are installed in the same manner as described with respect to the concrete form 10 shown in FIG. 1. The sheet material member 46 is positioned above the stakes 44 and then lowered until the lower surface of the strap means 60 engages and rests upon the ledge means 48 of the stakes 44. Due to the fact that the upper part of the stakes 44 are wedged" within the strap means 60 it will be understood that the sheet material member 46 must be urged downwardly in order to insure that the lower surface of the strap means 60 is disposed in contacting engagement with the ledge means 48. Application of this downward force is effected in a number of ways, one of which is through the use of the handle means 63. Where the sheet material member includes the apertures 66, the lower part of the sheet material member 46 is rotated clockwise, as viewed in FIG. 4, to permit the lower planar portion 56 to pass over or clear the tab portion 52. It will be understood that the apertures 66 and the tab portion 52 may be omitted from the concrete form 42 shown in FIG. 4 since the sheet material member 46 will be secured against vertical movement relative to the stakes 44 by the combined wedging action of the upper parts of the stakes 44 within strap means 60 and the biasing influence resulting from the convergence disposition of the upper planar portions, prior to installation of said member 46 upon said stakes 44, which causes the upper and lower planar portions to be firmly held against the adjacent sides of the stakes 44. Movement of the sheet material member 46 vertically relative to the stakes 44 is further resisted by forming roughened surface portions (not shown) either on appropriate surface portions of the stakes 44 or the sheet material member 46.

ln view of the foregoing descriptions, it is believed that the method and manner of installing the concrete form 68 shown in FIG. 8 will now be readily apparent and, thus, a description of the installation thereof is not deemed warranted.

it is now believed to be readily apparent that an improved concrete form and a sheet material member therefore has been described. The sheet material member and stakes are inexpensively manufactured, may be used within thick concrete slabs which are designed to support much heavier vehicle wheel loads and the like than is the case for those concrete forms in which the upper part of the sheet material member thereof includes an inverted Ushaped pocket, and may be used without danger of spalling or cracking occurring.

lclaim:

l. A concrete form of the type used in forming a key contraction joint between concrete slabs, said form comprising:

a plurality of spaced apart, aligned stakes, each of said stakes including a top and a ledge disposed beneath said top and projecting outwardly at a generally right angle to the longitudinal axis of its associated stake, said stakes adapted to be driven to a predetermined height so that the tops thereof are disposed along a first predetermined grade level; and,

an elongated rigid sheet material member suitable for attachment to said stakes, said elongated rigid sheet material member including:

upper and lower longitudinally extending planar portions and a longitudinally extending key deformation portion extending between and formed unitary with said upper and lower planar portions:

urging means for urging said rigid elongated sheet material member into contacting engagement against the sides of said stakes, said urging means including said planar portions one of which is formed, prior to attachment to said stakes, to lie in a plane which intersects a plane containing the other planar portion to form an included angle of not more than 117 so that upon subsequent attachment of said elongated sheet material member to said stakes said upper and lower planar portions lie in a common plane in a manner that presses said elongated rigid sheet material against said stakes to prevent vertical movement thereof:

a plurality of longitudinally spaced straps formed in one of said upper and lower planar portions, the spacing of said straps corresponding to the spacing between said stakes, each of said straps being disposed at least in partial encompassing engagement about a portion of a corresponding one of said stakes; and

ledge engaging means for abuttingly engaging said ledges, said ledges and said ledge engaging means cooperating to support said elongated rigid sheet material member along a second predetermined grade level.

2. A concrete form of the type described in claim 1 in which each of said straps includes a lower surface and said ledge engaging means comprises the lower surfaces of said straps.

3. A concrete form of the type described in claim 2 in which a portion of each of said straps is disposed in contacting engagement with one side of a corresponding one of said stakes,

member, with respect to said upper longitudinally extending.

planar portion.

4. A concrete form of the type described in claim 1 in which said ledge of each of said stakes includes a tab portion transversely disposed with respect to said stake and said ledge engaging means comprises a plurality of longitudinally spaced apertures, each of said apertures having a corresponding one of said tab portions disposed therein.

5. A concrete form of the type described in claim 1 in which said ledge of each of said stakes includes a tab portion transversely disposed with respect to said stake and said ledge engaging means comprises a longitudinally extending recess formed in said elongated rigid sheet material member, each of said tab portions being disposed within said recess.

6. A concrete form of the type described in claim 1 in which said straps are formed in said upper planar portion of said upper and lower longitudinally extending planar portions.

7. A concrete form of the type described in claim 6 in which:

said elongated rigid sheet material member also includes a plurality of longitudinally spaced lower straps formed in said lower planar portion and aligned with the straps formed in said upper planar portion, each of said lower straps having a lower surface;

said ledge comprises a tab portion transversely formed on said stake; and,

said ledge engaging means comprising the lower surfaces of the lower straps formed in said lower planar portion.

8. A concrete form of the type described in claim 1 in which said upper planar portion includes a folded over portion extending downwardly from the upper edge thereof and disposed against at least a part of said upper planar portion.

9. A concrete form of the type described in claim 8 in which said sheet member includes means formed thereon for increasing the frictional force resisting movement of the sheet member relative to said stakes, said means including roughened surface portions disposed in contacting engagement with said stakes.

10. A concrete form of the type described in claim 6 in which:

said elongated rigid sheet material member also includes a plurality of longitudinally spaced lower straps formed in said lower planar portion and aligned with the straps in said upper planar portion;

said ledge comprises a tab portion transversely formed on said stakes; and,

said ledge engaging means comprises the lower surface of said lower planar portion.

11. A concrete form of the type described in claim 10 in which said upper planar portion includes a folded over portion extending downwardly from the upper edge thereof and disposed against at least a part of said upper planar portion.

12. A concrete form of the type described in claim it in which said sheet member includes means formed thereon for increasing the frictional force resisting movement of the sheet member relative to said stakes, said means including roughened surface portions disposed in contacting engagement with said stakes.

1F I i t t 

1. A concrete form of the type used in forming a key contraction joint between concrete slabs, said form comprising: a plurality of spaced apart, aligned stakes, Each of said stakes including a top and a ledge disposed beneath said top and projecting outwardly at a generally right angle to the longitudinal axis of its associated stake, said stakes adapted to be driven to a predetermined height so that the tops thereof are disposed along a first predetermined grade level; and, an elongated rigid sheet material member suitable for attachment to said stakes, said elongated rigid sheet material member including: upper and lower longitudinally extending planar portions and a longitudinally extending key deformation portion extending between and formed unitary with said upper and lower planar portions: urging means for urging said rigid elongated sheet material member into contacting engagement against the sides of said stakes, said urging means including said planar portions one of which is formed, prior to attachment to said stakes, to lie in a plane which intersects a plane containing the other planar portion to form an included angle of not more than 117* so that upon subsequent attachment of said elongated sheet material member to said stakes said upper and lower planar portions lie in a common plane in a manner that presses said elongated rigid sheet material against said stakes to prevent vertical movement thereof: a plurality of longitudinally spaced straps formed in one of said upper and lower planar portions, the spacing of said straps corresponding to the spacing between said stakes, each of said straps being disposed at least in partial encompassing engagement about a portion of a corresponding one of said stakes; and ledge engaging means for abuttingly engaging said ledges, said ledges and said ledge engaging means cooperating to support said elongated rigid sheet material member along a second predetermined grade level.
 2. A concrete form of the type described in claim 1 in which each of said straps includes a lower surface and said ledge engaging means comprises the lower surfaces of said straps.
 3. A concrete form of the type described in claim 2 in which a portion of each of said straps is disposed in contacting engagement with one side of a corresponding one of said stakes, said portion of said straps including a generally vertically disposed part that is convergently disposed, taken in a direction proceeding toward the upper longitudinally extending planar portion of said elongated rigid sheet material member, with respect to said upper longitudinally extending planar portion.
 4. A concrete form of the type described in claim 1 in which said ledge of each of said stakes includes a tab portion transversely disposed with respect to said stake and said ledge engaging means comprises a plurality of longitudinally spaced apertures, each of said apertures having a corresponding one of said tab portions disposed therein.
 5. A concrete form of the type described in claim 1 in which said ledge of each of said stakes includes a tab portion transversely disposed with respect to said stake and said ledge engaging means comprises a longitudinally extending recess formed in said elongated rigid sheet material member, each of said tab portions being disposed within said recess.
 6. A concrete form of the type described in claim 1 in which said straps are formed in said upper planar portion of said upper and lower longitudinally extending planar portions.
 7. A concrete form of the type described in claim 6 in which: said elongated rigid sheet material member also includes a plurality of longitudinally spaced lower straps formed in said lower planar portion and aligned with the straps formed in said upper planar portion, each of said lower straps having a lower surface; said ledge comprises a tab portion transversely formed on said stake; and, said ledge engaging means comprising the lower surfaces of the lower straps formed in said lower planar portion.
 8. A concrete form of the type described in claim 1 in which said upper planar portion includes a folded oveR portion extending downwardly from the upper edge thereof and disposed against at least a part of said upper planar portion.
 9. A concrete form of the type described in claim 8 in which said sheet member includes means formed thereon for increasing the frictional force resisting movement of the sheet member relative to said stakes, said means including roughened surface portions disposed in contacting engagement with said stakes.
 10. A concrete form of the type described in claim 6 in which: said elongated rigid sheet material member also includes a plurality of longitudinally spaced lower straps formed in said lower planar portion and aligned with the straps in said upper planar portion; said ledge comprises a tab portion transversely formed on said stakes; and, said ledge engaging means comprises the lower surface of said lower planar portion.
 11. A concrete form of the type described in claim 10 in which said upper planar portion includes a folded over portion extending downwardly from the upper edge thereof and disposed against at least a part of said upper planar portion.
 12. A concrete form of the type described in claim 11 in which said sheet member includes means formed thereon for increasing the frictional force resisting movement of the sheet member relative to said stakes, said means including roughened surface portions disposed in contacting engagement with said stakes. 